Field of the Invention
The invention relates to processes for producing hollow bodies having a silicon-comprising shell, by converting at least one silane in a light arc or in a plasma, preferably in a plasma which is operated in a non-thermal equilibrium, or converting or pyrolysing it by means of electromagnetic waves, then dispersing in a solvent and distilling, and then converting in an etching operation.
Discussion of the Background
Metallic and semi-metallic particles such as silicon, for example, are important functional materials. Because of their property of intercalating lithium ions, they play an important role in the production of battery electrodes, catalysts or solar cells. In the case of batteries, for example lithium ion batteries, cycling stability with simultaneous prevention or inhibition of the formation of what are called dendrites or whiskers is a critical requirement. Inadequate cycling stability reduces the usability of the energy storage means in the event of frequent, often incomplete, charging and discharging, and whiskers can even destroy the battery as a result of internal short circuits. It is therefore very important to prevent such processes and to make functional material available in a large volume and in the purity required for the stated applications.
The application DE 102006059318 A1 proposes a process for producing porous silicon particles which exhibit typical photoluminescence as known in the literature. For this purpose, a plasma is produced by means of microwaves in a mixture of monosilane and argon or hydrogen, and the reaction product is thermally aftertreated in a hot wall reactor. The result is nanoparticles having solid amorphous cores. The nanoparticles can join together to form aggregates or agglomerates. By first converting the nanoparticles, aggregates or agglomerates with a solution of hydrofluoric acid in water and then with nitric acid in water, porous silicon particles are obtained after the acid has been consumed and the reaction has abated. Silicon particles of this kind have open pores which can be utilized, for example, as channels for the transport of liquids.
If such silicon particles were used in a battery as electrode material or as separator, the open pores would be large enough to promote the formation of whiskers which enter into typical transport operations for lithium ion batteries in the electrolyte and on the electrode material. The whiskers penetrate the pores gradually and establish an electrical connection between the battery electrodes, equivalent to an internal short circuit. A battery equipped with such a material would be unusable after a few charging cycles.